1. Field of the Invention
The present invention relates to an information recording processing apparatus, an information recording processing method and a computer program. In particular, the invention relates to an information recording processing apparatus, information recording processing method and computer program for performing data recording processing on an information recording medium such as an optical disk.
2. Description of the Related Art
Recording processing in accordance with a predetermined recording format is performed in recording data such as music data and image data as digital data on a recording medium. For example, an error detection/correction code is added to the original data to be recorded, which is then converted (encoded) to and recorded in a format in accordance with specific data writing/reading processing.
For example, in recording a signal on an optical disk, in addition to contents data such as a movie and a tune, format data is created with a signal required for generating a servo signal and/or reference clock signal available in data reading. Then, modulation processing in accordance with each data writing/reading method is performed thereon before the recording processing.
Typical examples of such modulation methods include EFM method used for a Compact Disc (CD) and a “MiniDisc (Registered Trademark of Sony Corporation)”, 8-16 modulation method used for a digital versatile disk (DVD), (1,7) RLL modulation method used for a magneto-optical disk, and 17PP modulation method used for a Blu-ray disk (BD).
For example, in (1,7) RLL modulation method, modulation is performed based on processing of modulating 2-bit data to 3-bit data. (1,7) RLL modulation method adopts a data conversion method which handles modulated data in accordance with the run length limit of RLL (1,7) in which the number of successive [0] in the modulated bit is one at the minimum and seven at the maximum. Notably, a conversion table is used in this conversion processing. A recording unit called recording frame with a synchronizing signal defined is created based on the modulation data and is recorded on an information recording medium such as an optical disk through a write signal processing circuit.
In the various kinds of modulation processing as described above, DC control is performed for data recording. For example, a DC-control bit is inserted at predetermined intervals in data such that the absolute value of a digital sum value (DSV) subject to modulation can be small before processing of creating write data is performed thereon.
The DC control processing is performed for control for keeping the low-frequency component of a Non Return to Zero Inverted (NRZI) signal as small as possible. In this case, the NRZI signal is a write signal onto a final disk. When a low-frequency component is included in a modulation signal, the low-frequency component leaks to a servo signal of an optical pickup in reading, resulting in an adverse effect on the servo. In order to prevent this, the DC control bit is inserted to keep the low-frequency component of the NRZI signal as small as possible. Notably, the NRZI (Non Return to Zero Inverted) signal is generated by inverting the sign of a pulse in accordance with [0] or [1] of modulated data.
A digital sum value (DSV) is an indicator for a DC balance of an NRZI-modulated signal, which is a write signal to an information recording medium. More specifically, the value including an accumulation of “−1” and “+1” where the bit [0] is handled as “−1” and bit [1] is handled as “+1” in a write bit stream (NRZI-converted signal). Then, for example, in order to reduce the alienation of the DSV from zero, “0” or “1” of the DC control bit is selectively inserted thereto.
In other words, the DSV is a value resulting from sequential additions of symbols from the starting point in a wave train where the symbols 1 and 0 corresponding to bit values are handled as +1 point and −1 point, respectively, in a recording wave train. The DSV is used as a criterion for evaluation of a direct-current component of a modulated signal. When the absolute value of a DSV is small, the direct-current component or low-frequency component is small. Therefore, the value of the DC control bit to be inserted for keeping the absolute value of the DSV small is determined. The descriptions on a general DC control bit and a DSV are disclosed in “Hikari Disk (Optical Disk),” Rajio Gijutsu Sha, Pg. 180.
On the other hand, in data reading from an optical disk, when the size of the pit formed on a disk is small in comparison with the magnitude of a light beam, a change of reflected light is small, resulting in a small amplitude of the read signal. In other words, a small pit length and/or pit interval on a disk (which raises a spatial frequency) tends to cause a small read amplitude. A change in amplitude for a spatial frequency is called Modulation Transfer Function (MTF). In this way, it is known that a read waveform has a property of having an amplitude of a read signal attenuating in a high frequency due to the optical characteristic (MTF). The general description on reading processing on an optical disk is disclosed in, for example, “DVD Dbkuhon (DVD reader),” Ohmsha, Pg. 98.
As described above, for control for keeping the low-frequency component of an NRZI (non Return to Zero Inverted) signal, which is a write signal, as small as possible in data recording processing, a DSV is a sum of symbols from a starting point in a wave train where symbols 1 and 0 corresponding to bit values of a write bit stream (NRZI-converted signal) are +1 and −1 points, respectively. Then, the value of the DC control bit is selectively inserted such that the alienation of the DSV value from zero can be smaller.
However, DSV control in the past is only based on the number of data with symbols “1” and “0” independently of the height of the frequency of a signal to be recorded. In this case, when, for example, write data at a high frequency goes on for the symbol, “1”, and write data at a low frequency goes on for the symbol, “0”, the control processing controls the absolute value of the DSV closely to zero (0). However, in data reading, the average amplitude of a read signal of the data part corresponding to symbol, “1” is smaller than the average amplitude of a read signal of the data part corresponding to the symbol, “0”. As a result, the read signal carries a low-frequency component biased to the side of symbol, “0”, and proper control over a low-frequency component may not be performed, which is a problem.
Accordingly, it is desirable to propose an information recording processing apparatus, information recording processing method and computer program, which can implement proper control over a low-frequency component even when the height of the frequencies of write data corresponding to symbols “1” and “0” is out of balance.